1. Field of the Invention
The invention refers to grate elements forming parts of bottoms of grates and to grates composed of such elements designed for the treatment or combustion of solid material with gas at high temperatures. Such grate elements which are provided in the way of grate bars, grate plates or grate blocks and dimensioned to avoid warping under thermal expansion are composed in an appropriate manner to form such grate bottoms and to determine the grate's working area. These bottoms carry said solid material and in most cases convey it either by their inclination or by their motion. Conveying may also take place by means of scrapers or by said gas with the aid of which said treatment is carried out. The bottoms are provided with openings for supplying the gas to the solid material. The openings are normally formed between grate bars or are part of grate plates or grate blocks.
2. Description of Prior Art
In order to meet special requirements of the gas penetration so-called jet bottoms are provided for grates. If high processing temperatures are necessary such jet bottoms consist of ceramic material. However, such material does not meet the requirements of mobile grates due to their low mechanical strength.
In conventional grate bottoms different ways of fulfilling the requirements of inner cooling and defined resistance for an even distribution of said gas into the layer of solids covering the grate bottom have been used. Cooling ribs or cooling channels provided at the gas inlet side of the grate bottom have been proposed and shown, e.g. in published German Patent Application Nos. 3 213 294 and 3 230 597.
The relative open grate area is a characterizing feature of the grate's resistance against gas penetration. E.g. 5% open grate area means that the supplied gas will develop a velocity within said openings 20 times as high as underneath said grate bottom, i.e. at the inlet for the gas into the grate elements. This gas velocity causes an upward force which may be greater than the grate plate's weight. In the case of pivoted grate plates according to published German Patent Application No. 1 758 067 this force is balanced by an additional weight.
High gas velocities emerging perpendicular to the working area may not be desirable. According to published German Patent Application No. 3 313 615 a grate block for an oscillating grate may therefore have an opening ejecting said gas approximately horizontally.
The advantages of such essentially horizontal air jets are described in U.S. Pat. No. 3,304,619. The jets effect the conveying of the solid material and improve the heat transfer in cooling processes. However, a heat resistant grate plate realizing these advantages is neither described nor proposed by this publication.
In conventional grates inclined slots arranged transversely with respect to the conveying direction are formed between single grate bars. Contrary to grate plates bedded directly on grate beams, these grate bars require intermediate brackets placed longitudinally on the grate beams. Such design, however, impedes an airtight attachment of gas compartments to the grate, especially at increased gas pressure, as well as the transmission of oscillating or travelling motions of the respective types of grates for conveying the solid material to be treated.
It is further known that a small open grate area in connection with a high velocity of the gas will diminish the amount of solids dribbling through the grate openings. However, such a grate still requires expensive means for the tapping of dribblings from said compartments and their further handling.
Only jet bottoms which e.g. have overlapping covers above said openings prevent solids from reaching said openings even when the gas supply is interrupted.
Published German Patent Application No. 2 005 869 describes a louvre type staired wall conveying powder material transverse to the penetration direction of the processing gas. The louvres carrying the powder are slightly lifted against gravity so that no powder can dribble out.
Both examples show in principle that impediments orientated to gravity will avoid dribblings. The solution with louvres, however, does not realize a sufficient resistance against gas penetration as is necessary for even gas distribution.
3. Objects of the Invention
It is therefore an essential object of the invention to suggest a grate element for a grate bottom being mechanically highly resistant and combining the advantages known from various designs of grate bars, grate plates, grate blocks or jet bottoms with respect to inner cooling, resistance against gas penetration and prevention of dribblings.
It is a further object of the invention to suggest grate plates which can be manufactured by casting and still provide openings finely distributed, inclined and arranged transversely with respect to the conveying direction.
It is yet another object of the invention to suggest a grate design bedding grate plates directly on transverse grate beams without intermediate brackets, thus facilitating the attachment of gas compartments and the exchange of said grate plates even during operation of the grates.